Electrocatalytic Kinetics Research Articles

Identifying the impact of Fe nanoparticles encapsulated by nitrogen-doped carbon to Fe single atom sites for boosting oxygen reduction reaction toward Zn-air batteries

Herein, a proof-of-concept study on the evaluation of Fe nanoparticles (Fe NPs) encapsulated by nitrogen-doped carbon to Fe single atoms (Fe SAs) for boosting the oxygen reduction reaction (ORR) catalytic activity toward Zn-air batteries was reported. Specifically, unlike Fe SAs encapsulated by nitrogen-doped carbon (Fe SAs@NC), the Fe SAs and Fe NPs co-embedded in nitrogen-doped carbon (Fe SAs/NPs@NC) derived from a pyrolysis and acid dissolution protocols exhibits excellent ORR performance with good stability and remarkable methanol tolerance in alkaline solutions. Combining a series of experimental analyses, the strong interaction between the atomically dispersed Fe-Nx and adjacent Fe NPs in altering the electronic structure of isolated Fe-Nx sites could weaken the binding energies of the ORR intermediates on Fe SAs/NPs@NC, resulting in an enhanced electrocatalytic kinetics than Fe SAs@NC and Pt/C catalysts. This strategy not only offers a new way for synthesis highly efficient Fe-N/C catalysts toward ORR, but also provides the new insights into the understanding of the mechanism of adjacent Fe NPs encapsulated by nitrogen-doped carbon to Fe SAs sites.

Construction of NiS@CoFeMoO4/NF nanosheet heterostructures for efficient overall water splitting

Inexpensive and robust earth-abundant electrocatalysts with excellent electrocatalytic reaction kinetics must be developed to realize electrochemical water-splitting. In this study, nickel sulfide@cobalt iron-molybdenum oxide (NiS@CoFeMoO4) nanosheet heterostructures supported on nickel foam were fabricated. The as-built NiS@CoFeMoO4/NF with a sheet-on-sheet morphology delivered a current density of 10 mA cm−2 with a low overpotential of 72 and 200 mV for the hydrogen evolution and oxygen evolution reactions, respectively. The formation of a synergistic heterostructure between NiS and CoFeMoO4/NF via interfacial engineering facilitated the generation of a micro-mesoporous surface and modulation of the charge density at interfaces. Consequently, this configuration outperformed many non-precious-metal-based catalysts as an electrocatalyst for water oxidation.

Efficient synthesis of H2O2via oxygen reduction over PANI driven by kinetics regulation of carbon dots

Electrocatalytic two-electron (2e−) oxygen reduction reaction (ORR) is a promising method to realize the sustainable production of H2O2. However, the 4e− pathway competes with 2e− ORR, presenting a challenge to the design of highly selective, low-cost catalysts. In addition to the design of active sites, the regulation on electrocatalytic kinetics is another strategy to get ideal 2e− ORR route. Here, cobalt doped carbon dots (CDs-Co) were used to regulate the electron transport kinetics on polyaniline (PANI) by constructing p-n heterojunction. The electron transfer kinetics and oxygen molecular activation process on PANI/CDs-Co were studied and analyzed using the transient photo-induced voltage (TPV) and pulse voltage-induced current (PVC) technologies, respectively. These results show that CDs-Co not only reduces the over-potential of oxygen molecular activation, but also reduces the transient electron concentration on PANI, which effectively improves the selectivity and activity of H2O2 production via ORR. The obtained PANI/CDs-Co-2 shows a H2O2 selectivity nearly 100.0% higher than that of PANI (76.3%). And it exhibits a H2O2 productivity of 3.5 mol g−1cat h−1 at 0 V vs. RHE tested by gas diffusion electrode device. This work provides new insights for the design of 2e− ORR catalysts and the study of electrocatalytic kinetics.

Effect of constituent cations on the electrocatalytic oxygen evolution reaction in high-entropy oxide (Mg0.2Fe0.2Co0.2Ni0.2Cu0.2)O

To find core cations driving a high electrocatalytic activity in high-entropy oxide (HEO), the medium-entropy oxides (MEOs) subtracting each cation from the HEO are prepared and evaluated toward the alkaline water-splitting oxygen evolution reaction (OER) activity. • The core cations driving a high electrocatalytic activity in the high-entropy oxide are identified. • The high and medium-entropy oxides by subtracting each cation from the HEO are prepared. • It is found that Co 3+ is the core ion driving the high OER activity. • It is regarded that Cu 2+ ions prevent the conversion of Co or Fe cations from 2 + to 3 + . • Maximizing the concentration of Co 3+ within electrocatalysts is an effective design strategy. The electrocatalytic electrode kinetics should be controlled to overcome overpotentials for the hydrogen generation via water electrolysis, which consists of the cathodic hydrogen evolution reaction (HER) and the anodic oxygen evolution reaction (OER). Although transition metal catalysts that can replace noble metal catalysts are presented, more studies are still required in terms of stability and activity. Since the compositional diversity can provide a new breakthrough in that area, a high-entropy oxide (HEO) with five cations, (Mg 0.2 Fe 0.2 Co 0.2 Ni 0.2 Cu 0.2 )O, is applied as a promising electrocatalyst toward the OER in this study. For the HEO electrocatalysts, unveiling the effect of constituent cations on the OER activity and finding core cations driving the high OER activity come as a major issue. For it, in this work, the medium-entropy oxides (MEOs) with four cations are prepared by subtracting each cation (Mg, Fe, Co, Ni, or Cu) from the HEO, exhibiting homogeneous morphology, equiatomic composition, and single-phase rocksalt structure. As a result, it is found that the highest concentration of Co 3+ in the MEO (w/o Cu) leads to the best OER activity, and thus Co 3+ is the core ion driving the high OER activity. Furthermore, it is regarded that Cu 2+ ions prevent the conversion of Co or Fe cations from 2 + to 3 + in the HEO and MEOs. Accordingly, maximizing the concentration of Co 3+ within electrocatalysts is suggested as an effective design strategy for the high-efficiency electrocatalysts based on high or medium entropy materials.

Effect of Fe doping on Co-S/carbon cloth as bifunctional electrocatalyst for enhanced water splitting

• Fe-Co-S nanoflakes were successfully grown on the carbon cloth. • Fe doping can tuning the electronic structure of the Fe-Co-S/CC. • The Fe-Co-S/CC-75 shows superior alkaline HER and OER catalytic kinetics. • The Fe-Co-S/CC-75 as bifunctional electrocatalyst exhibits excellent electrocatalytic capability for overall water splitting. Considering the sluggish kinetics of oxygen evolution reaction (OER), rational design of HER and OER electrocatalysts with high catalytic activity in alkaline conditions remains a challenge for achieving large-scale commercial application of water splitting. In this paper, the Fe-Co-S nanoflakes grown on the carbon cloth (Fe-Co-S/CC) were fabricated by hydrothermal method and subsequent annealing treatment to enhance the crystallinity. Fe doping could regulate the d orbital electron density to improve the electrocatalytic kinetics for HER and OER. The hierarchical Fe-Co-S/CC as a binder-free electrode with more active sites and enhanced electronic conductivity exhibits low overpotentials of 258 mV and 320 mV for the oxygen evolution reaction (OER) and hydrogen evolution overpotential (HER) in an alkaline solution at the current densities of 10 mA cm −2 , respectively. Meanwhile, the Tafel slope is 61.20 mV dec -1 and 82.60 mV dec -1 , along with long-term stability for over 48 h.

Design of Ni(OH)2 nano-boxes@CuS nanosheets hollow hierarchical structure to achieve synergistic catalysis for high sensitivity dopamine electrochemical sensing

Inspired by electrocatalytic kinetics, the design of hollow hierarchical structure through the integration of three-dimensional (3D) scaffolds and two-dimensional (2D) sheet-like materials was considered as an effective approach to achieve superior electrocatalytic activity. Ni(OH)2 nano-boxes@CuS nanosheets hollow hierarchical structure (Ni(OH)2 NBs@CuS NSs HHS) was synthesized by a sulfidation involved coordinated etching and precipitation (CEP) process for the first time. Interestingly, CuS nanosheets were vertically distributed on Ni(OH)2 NBs. As a sensitive electrode for dopamine, Ni(OH)2 NBs@CuS NSs HHS modified glassy carbon electrode (GCE) showed a sensitivity as high as 1011.7 μA mM−1 cm−2, which was greater than those of Ni(OH)2 NBs@CuS NSs fragmentized HHS/GCE (Ni(OH)2 NBs@CuS NSs FHHS/GCE, 354.1 and 717.2 μA mM−1 cm−2), CuS NBs/GCE (646.2 μA mM−1 cm−2) and Ni(OH)2 NBs/GCE (472.1 and 848.2 μA mM−1 cm−2). Moreover, Ni(OH)2 NBs@CuS NSs HHS/GCE showed an ultralow detection limit of 3.2 nM. According to theoretical calculation, the excellent electroactivity was attributed to the enhanced kinetics issued from the combination of 3D Ni(OH)2 NBs and 2D CuS NSs. Ni(OH)2 NBs@CuS NSs HHS was expected as an ideal electrocatalyst for dopamine electrochemical sensing, and the integrating of transition metal-based hollow scaffolds and 2D materials provided new thought to acquire high electrocatalystic activity.

Highly Efficient Electrocatalytic Oxygen Evolution Over Atomically Dispersed Synergistic Ni/Co Dual Sites

AbstractSingle‐atom catalysts (SACs) are being pursued as economical electrocatalysts. However, their low active‐site loading, poor interactions, and unclear catalytic mechanism call for significant advances. Herein, atomically dispersed Ni/Co dual sites anchored on nitrogen‐doped carbon (a‐NiCo/NC) hollow prisms are rationally designed and synthesized. Benefiting from the atomically dispersed dual‐metal sites and their synergistic interactions, the obtained a‐NiCo/NC sample exhibits superior electrocatalytic activity and kinetics towards the oxygen evolution reaction. Moreover, density functional theory calculations indicate that the strong synergistic interactions from heteronuclear paired Ni/Co dual sites lead to the optimization of the electronic structure and the reduced reaction energy barrier. This work provides a promising strategy for the synthesis of high‐efficiency atomically dispersed dual‐site SACs in the field of electrochemical energy storage and conversion.

Highly Efficient Electrocatalytic Oxygen Evolution Over Atomically Dispersed Synergistic Ni/Co Dual Sites

Single-atom catalysts (SACs) are being pursued as economical electrocatalysts. However, their low active-site loading, poor interactions, and unclear catalytic mechanism call for significant advances. Herein, atomically dispersed Ni/Co dual sites anchored on nitrogen-doped carbon (a-NiCo/NC) hollow prisms are rationally designed and synthesized. Benefiting from the atomically dispersed dual-metal sites and their synergistic interactions, the obtained a-NiCo/NC sample exhibits superior electrocatalytic activity and kinetics towards the oxygen evolution reaction. Moreover, density functional theory calculations indicate that the strong synergistic interactions from heteronuclear paired Ni/Co dual sites lead to the optimization of the electronic structure and the reduced reaction energy barrier. This work provides a promising strategy for the synthesis of high-efficiency atomically dispersed dual-site SACs in the field of electrochemical energy storage and conversion.

Chemical Energy‐Driven Lithiation Preparation of Defect‐Rich Transition Metal Nanostructures for Electrocatalytic Hydrogen Evolution

Transition metal nanostructures are widely regarded as important catalysts to replace the precious metal Pt for hydrogen evolution reaction (HER) in water splitting. However, it is difficult to obtain uniform-sized and ultrafine metal nanograins through general high-temperature reduction and sintering processes. Herein, a novel method of chemical energy-driven lithiation is introduced to synthesize transition metal nanostructures. By taking advantage of the slow crystallization kinetics at room temperature, more surface and boundary defects can be generated and remained, which reduce the atomic coordination number and tune the electronic structure and adsorption free energy of the metals. The obtained Ni nanostructures therein exhibit excellent HER performance. In addition, the bimetal of Co and Ni shows better electrocatalytic kinetics than individual Ni and Co nanostructures, reaching 100mAcm-2 at a low overpotential of 127mV. The high HER performance originates from well-formed synergistic effect between Ni and Co by tuning the electronic structures. Density functional theory simulations confirm that the bimetallic NiCo possesses a low Gibbs free energy of hydrogen adsorption, which are conducive to enhance its intrinsic activity. This work provides a general strategy that enables simultaneous defect engineering and electronic modulation of transition metal catalysts to achieve an enhancement in HER performance.

Fe-Fe3C Functionalized Few-Layer Graphene Sheet Nanocomposites for an Efficient Electrocatalyst of the Oxygen Reduction Reaction.

Preparation of a high-efficiency, low-cost, and environmentally friendly non-precious metal catalyst for the oxygen reduction reaction (ORR) is highly desirable in fuel cells. Herein, a Fe–Fe3C-functionalized few-layer graphene sheet (Fe/Fe3C/FLG) nanocomposite was fabricated through the vacuum heat treatment technique using ferric nitrate and glucose as the precursors and exhibited a high-performance ORR electrocatalyst. Multiple characterizations confirm that the nanosized Fe particles with the Fe3C interface are uniformly distributed in the FLGs. Electrocatalytic kinetics investigation of the nanocomposite indicates that the electron transfer process is a four-electron pathway. The formation of the Fe3C interface between the Fe nanoparticles and FLGs may promote the electron transfer from the Fe to FLGs. Furthermore, the Fe/Fe3C/FLG nanocomposite not only exhibits high ORR catalytic activity but also displays desirable stability. Consequently, the obtained Fe/Fe3C/FLG nanocomposite might be a promising non-precious, cheap, and high-efficiency catalyst for fuel cells.

Chromium-Rich Core-Shell Cr x Ir1-X O2 Nanotubes for Highly Efficient Oxygen Evolution Reaction in Alkaline Solution

Considering the growing attention to oxygen evolution reaction (OER) as a key role in clean energy through electrocatalytic water splitting, advanced materials for water oxidation are central to the area of renewable energy. In general, the OER process, involved four electron and four proton coupled electrochemical reaction, demands higher kinetics to overcome an overpotential than HER (hydrogen evolution reaction). For this aspect, significant research efforts have been devoted to developing efficient OER electrocatalyst with enhanced electrocatalytic kinetics and long-term durability.Here we present the synthetic processes and physical/electrochemical characterization of Cr x Ir1-x O2 nanotubes (NTs). Those NTs are synthesized through electrospinning, a simple way to facilitate 1D nanostructure, and post-thermal annealing process with different annealing speed (°C /min). As-prepared Cr x Ir1-x O2 NTs at the optimized conditions have shown outstanding OER electrocatalytic activity in alkaline media from the viewpoints of overpotential and Tafel slope as well as durability. The morphology and compositions of Cr x Ir1-x O2 were characterized by a field emission scanning electron microscope (FESEM) equipped with an energy dispersive X-ray spectrometer (EDS), high-resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS). The crystalline structures of the prepared Cr x Ir1-x O2 are investigated through high-resolution X-ray diffraction (XRD). Electrochemical activities for oxygen evolution reaction (OER) are studied with rotating disk electrode (RDE) voltammetry in N2-saturated 1.0 M KOH (aq); and compared with those of iridium single component oxides (IrOx and IrO2) and commercial iridium (cIr, counterparts in OER electrocatalysts).This work was financially supported by the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT or by the Ministry of Education (NRF-2019R1F1A1059969, NRF-2018R1A6A1A03025340, NRF-2020R1A2B5B01001984, and NRF-2019R1F1A1062799).

Engineering of Co3O4@Ni2P heterostructure as trifunctional electrocatalysts for rechargeable zinc-air battery and self-powered overall water splitting

Rational design of highly efficient, robust and nonprecious electrocatalysts for the oxygen reduction reaction (ORR), oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is highly demanded and challenging. Here, heterostructural Co3O4@Ni2P arrays with numerous reaction sites, unique interfacial electronic structure and fast charge transfer kinetics are developed as electrocatalysts for rechargeable Zn-air batteries and overall water splitting. Both density functional theory calculation and X-ray absorption fine structure analysis manifest that the synergistic structural and abundant electronic modulations interfaces are formed, thus simultaneously promoting the electrocatalytic kinetics, activities and stabilities. Specifically, it can achieve an ultralow overpotential of 270 mV and 28 mV at 10 mA cm−2 for OER and HER, respectively. The water electrolyzer delivers a current density of 10 mA cm−2 at 1.563 V; furthermore, rechargeable Zn-air batteries triggered by this heterostructure can achieve excellent cyclic stability of 177 h (2 h per cycle) at 10 mA cm−2; both devices are superior to the Pt/C + Ir/C. This work not only designs an efficient trifunctional electrocatalyst but also paves an avenue to understand the heterostructure engineering for catalysts development and disclose the underlying relationship of interfacial electronic structures and catalytic properties.

Engineering high-entropy alloy nanowires network for alcohol electrooxidation

High-entropy noble metals have attracted significant attention owning to their unique physicochemicalcharacteristics. Here we report a simple method for the preparation of high-entropy PdPtCuAgAu nanowire networks using carboxyl-functionalized surfactants as soft templates. This PdPtCuAgAu alloy electrocatalysts possess synergetic compositional (e.g., high-entropy effect, sluggish diffusion effect, and lattice distortion effect) and structural (anisotropic and thin nanowires) advantages. The PdPtCuAgAu alloy electrocatalysts exhibit significantly enhanced electrocatalytic performance toward ethanol oxidation reaction, including high mass activity (7.7 A mgPd+Pt−1), superior stability/durability, anti-poisoning ability, and fine electrocatalytic kinetics. Similar improvements in electrocatalytic performance are also seen in reactions involving other alcohols such as ethylene glycol and methanol. The high-entropy characteristics synergistically attributed to the enhanced electrocatalytic ability for different reaction process. This approach for the synthesis of high-entropy alloys will provide a new route to rationally design other high-entropy nanocatalysts with desired morphologies/structure and functions for a wide range of (electro)catalytic applications.

Hierarchical nanocomposites of nickel/iron-layered double hydroxide ultrathin nanosheets strong-coupled with nanocarbon networks for enhanced oxygen evolution reaction

Nickel/iron-layered double hydroxide (NiFe-LDH) for oxygen evolution reaction (OER) was hindered insufficient active sites, low inherent conductivity and poor stability. Herein, we innovatively report a facile and cost-effective in situ synthesis strategy to prepare ultrathin NiFe-LDH nanosheets coupled onto hierarchical nanocarbon networks consisting of carbon nanotube and graphene nanoribbon (NiFe-LDH/CNT@GNR) forming a porous interconnected nanocomposite. Partial unzipping of CNT induced by strong oxidation leads to the creation of GNR nanolayers tightly attached to the retained CNT framework, where GNR achieves high surface areas to load NiFe-LDH nanosheets and inner CNT still enables high conductivity. The CNT@GNR nanocarbon network not only enhances accessible electrochemical active area and mass transfer, but also provides high-efficiency conductive brackets with interlinked electron transfer pathways and achieve the strong interface coupling with NiFe-LDH nanosheets, synergistically resulting in rapid electrocatalytic kinetics. Moreover, NiFe-LDH nanosheets are tightly anchored on the surface of nanocarbon networks, greatly enhanced the stability of NiFe-LDH. NiFe-LDH/CNT@GNR exhibits remarkable OER activity with a low overpotential of 261 mV at 10 mA cm−2, Tafel slope of 78 mV dec−1, and high stability for up to 17 h, superior to most LDH-based OER catalysts reported, and even better than commercial RuO2. Therefore, the facile synthesis and excellent hierarchical architecture endow NiFe-LDH/CNT@GNR nanocomposites as advanced electrocatalysts for outstanding OER performance. Most importantly, the design provides a simple but universal strategy to yield high performance of NiFe-LDH catalysts, facilitating the commercial process of non-noble catalysts for OER.

Iridium‐Functionalized Metal‐Organic Framework Nanocrystals Interconnected by Carbon Nanotubes Competent for Electrocatalytic Water Oxidation

AbstractNanocrystals of a zirconium‐based metal‐organic framework (MOF), UiO‐66, are grown on the surface of the carboxylic acid‐functionalized multi‐walled carbon nanotubes (CNT) at room temperature to synthesize the UiO‐66‐CNT nanocomposites with tunable MOF‐to‐CNT ratios. The porosity, crystallinity, morphology, and electrical conductivity of the nanocomposite are characterized. Spatially dispersed iridium sites are thereafter installed on the defect sites presented within the entire UiO‐66 crystals in these nanocomposites by a self‐limiting solution‐phase approach. The resulting Ir‐functionalized UiO‐66, CNT, and UiO‐66‐CNT nanocomposites are served as the electrocatalysts for water oxidation in acidic aqueous solutions. By utilizing the redox‐hopping pathways to transport electrons within the Ir‐functionalized MOF crystals as well as the electronic conduction between MOF crystals provided by CNT, the nanocomposite with the optimal MOF‐to‐CNT ratio can outperform both the Ir‐functionalized UiO‐66 and CNT. Electrochemical impedance spectroscopy (EIS) is utilized to probe the reaction kinetics occurring on the decorated iridium sites and the transporting behaviors of electrons/ions within these catalytic thin films. For the first time, the electrocatalytic kinetics and the transporting limitations within the MOF‐based thin film can be decoupled with the help of EIS technique. Post‐electrocatalysis characterizations of the nanocomposite after water oxidation are also performed.

Porous boron-doped diamond for efficient electrocatalytic elimination of azo dye Orange G

Boron-doped diamond (BDD) is an ideal material being used for electrocatalytic elimination of environmental organic pollutants, but the commercial BDD electrodes have several limitations such as small electroactive area, slow mass transfer and low pollutants decomposition efficiency. In this paper, porous BDD electrodes with different pore sizes were synthesized by replicating porous Ti (powder metallurgy) with three-dimensional interoperable network structure, controllable aperture and porosity in a hot filament chemical vapor deposition (HFCVD) system. Various aspects of porous BDD with different pore sizes in terms of physicochemical properties, electrocatalytic reaction kinetics and mass transfer, which had not been previously researched, were systematically discussed. Meanwhile, some fundamental issues such as the enhancement mechanism of reaction kinetics of porous electrodes, the electrocatalytic degradation mechanism and pathways of contaminants on flat and porous BDD electrodes have been thoroughly investigated. Porous BDD electrodes had significantly higher Orange G (OG) electrocatalytic apparent reaction rate constants (up to 5.55 times that with flat BDD) and dramatically lower electrical energy per order (down to 25% that with flat BDD) for pollutant removal due to their increased electroactive area, reduced charge transfer resistance, and enhanced mass transfer. The electroanalysis, hydroxyl radical quenching and intermediates identification revealed the electrocatalytic degradation mechanism and reaction pathways of OG. In general, Porous BDD electrodes combined the properties of BDD and porous Ti, making them a commercially applicable and efficient material with high electroactive area, high electrocatalytic activity, long-term stability and low cost for electrocatalytic elimination of environmental organic pollutants.

Silver decorated hydroxides electrocatalysts for efficient oxygen evolution reaction

Electrocatalysts play a pivotal role in electrochemical water splitting, where the development of efficient oxygen evolution reaction (OER) electrocatalysts remains challenging. Here, we report a facile one-step blending approach to synthesize efficient and durable OER electrocatalysts of silver decorated hydroxides (Ag@hydroxides). The general efficacy of this methodology is demonstrated in five hydroxides, in form of powders or self-supported electrodes. The decoration of Ag lowers the overpotentials by 41–56 mV, rendering Ag@NiFe LDH among the most active OER catalysts. It requires an overpotential of 246 mV only to deliver a current density of 10 mA cm−2. Under industrial electrolysis conditions (30 wt% KOH and 80 °C), the cell voltage is 1.76 V for 500 mA cm−2. It is 270 mV lower than the intact nickel mesh, corresponding to a 9% improvement in the energy conversion efficiency. Furthermore, by combining spectroscopic analysis and theoretical calculation we unravel that the strong interfacial charge transfer is the root cause for the promoting catalytic activity, where the binding energies of catalytic intermediates are optimized. This work provides a facile and ease-to-scale-up approach for the synthesis of efficient and durable electrocatalysts and demonstrates the power of regulating the interface in improving electrocatalytic kinetics.

Deposition of Cu on Ni3S2 nanomembranes with simply spontaneous replacement reaction for enhanced hydrogen evolution reaction

The integration of metal with transition metal disulfides (TMDs) is considered as one of the promising strategies to improve the hydrogen evolution reaction (HER) performance of TMDs through modifying the electrocatalytic kinetics. However, the deposition of metal on TMDs often requires reducing agents, surfactants or extra energy consumption, which increases the synthesis complexity and application cost. Here, metallic Cu was deposited on the Ni3S2 nanomembranes in situ grown on nickel foam (Cu/Ni3S2/NF), which is achieved through a simple replacement reaction between Cu2+ and Ni at room temperature. The microstructure characterizations reveal that Cu was uniformly distributed on Ni3S2 nanomembranes in amorphism. The XPS measurements indicate that the decoration of Cu makes the enrichment and depletion of electrons in S and Ni, respectively. Electrochemical testing shows that Cu/Ni3S2/NF has superior electrocatalytic activity with low overpotential of 130 mV to deliver a current density of 10 mA cm−2 for HER in 1.0 M KOH, and a Tafel slope of 84.19 mV dec-1. Furthermore, Cu/Ni3S2/NF possesses excellent electrocatalytic stability with nearly no increase in overpotential after continuously catalyzing for 48 h at a current density of −50 mA cm−2. This work paves the ways to prepare high-performance electrocatalysts based on metal modified TMDs with a simple and low-cost route, which is expected to promote the practical HER application of TMDs.

Facile synthesis of hierarchical Nb-Doped Mo–Ni–S nanospheres as efficient electrocatalyst toward hydrogen generation in alkaline media

Exploring highly-efficient and inexpensive electrocatalysts toward hydrogen evolution reaction (HER) in alkaline electrolyte act as pivotal role on boosting the development of hydrogen energy. Doping strategy has been regarded as an effective approach to accelerate electrocatalytic kinetics. Herein, transition metal doping method is applied to develop hierarchical molybdenum-nickel bimetallic sulfide nanospheres for HER. The unique spherical structure and synergistic effects between different elements are favorable for improving the electrocatalytic performance by exposing abundant active sites and electronic interactions. Therefore, the synthesized Nb–Mo–Ni–S (Nb-MNS) exhibits outstanding HER performance with overpotentials of 49 mV and 135 mV to deliver 10 mA cm −2 and 100 mA cm −2 , respectively. Significantly, Nb-MNS displays superior stability of 48 h with the current densities changed from 40 mA cm −2 to 120 mA cm −2 . This work provides a promising avenue to design transition metal sulfides for energy conversion reactions. The synthesized Nb-MoNiS (Nb-MNS) exhibits outstanding HER performance with overpotential 49 mV and 135 mV to deliver 10 mA cm-2 and 100 mA cm-2, respectively. • One-step synthesis strategy is developed to prepare advanced molybdenum-nickel bimetallic sulfides on NF. • Nb doping is an efficient avenue to improve the electrocatalytic performance of the prepared catalyst. • The synthesized Nb-MNS exhibits outstanding HER performance.

Manipulating Electrocatalytic Polysulfide Redox Kinetics by 1D Core–Shell Like Composite for Lithium–Sulfur Batteries

AbstractAlthough lithium–sulfur batteries have high theoretical energy density of 2600 Wh kg−1, the sluggish redox kinetics of soluble liquid polysulfide intermediates during discharge and charge is one of the main reasons for their limited battery performance. Designing highly efficient electrocatalysts with a core–shell like structure for accelerating polysulfide conversion is vital for the development of Li–S batteries. Herein, core–shell MoSe2@C nanorods are proposed to manipulate electrocatalytic polysulfide redox kinetics, thereby improving the Li–S battery performance. The 1D MoSe2@C is synthesized via a facile hydrothermal and subsequent selenization reaction. The electrocatalysis of MoSe2 is confirmed by the analysis of symmetric batteries, Tafel curves, changes of activation energy, and lithium‐ion diffusion. Density functional theory calculations also prove the low Gibbs free energy of the reaction pathway and the lithium‐ion diffusion barrier. Therefore, the Li–S batteries using MoSe2 electrocatalyst exhibit an excellent rate performance of 560 mAh g−1 at 1 C with a high sulfur loading of 3.4 mg cm−2 and an areal capacity of 4.7 mAh cm−2 at a high sulfur loading of 4.7 mg cm−2 under lean electrolyte conditions. This work provides a deeper insight into regulation of polysulfide redox kinetics in electrocatalysts for Li–S batteries.